Just as your gas mileage will vary depending on where and how you drive, so it goes with the life of brake pads (or linings), the friction material that gets pressed against a metal disc or drum to stop your vehicle.

If you drive only 8,000 miles a year but it’s mainly in a crowded urban area such as Chicago, Boston or Washington, D.C., you will need to replace brake pads more often than someone who drives 28,000 miles a year across the flatlands of Nebraska. You use your brakes a lot more in urban driving than on a rural highway.

Unfortunately, there is no clear-cut schedule that tells you when it’s time to replace the brakes, so you need to rely on your ears and the advice of an experienced automotive technician. Most vehicles should have their tires rotated at least every six months, and that is a good time to have the brakes inspected, as well. A mechanic can check the thickness of the pads and the condition of the brake hardware to spot wear.

Many cars have built-in wear sensors that scrape against a brake disc when the linings needed replacing. The driver will hear an annoying screeching sound when they apply the brakes (or when the brakes are released on some vehicles).

Those sensors aren’t on every vehicle, so drivers should listen for squeaks, squeals, grinding (often a sign that brake pads are entirely gone) and other noises that indicate wear. Some minor noises can be eliminated by cleaning the brakes, but persistent, prominent noises usually mean parts are worn. Other signs are pulsations through the brake pedal, longer stopping distances, or when you apply the brakes your foot goes down further, closer to the floor. Because brake linings wear gradually, you may not notice the demise in performance, so that’s where the experienced eye of a mechanic can help.

All cars have a brake warning light that comes on for a few seconds every time you start your car. If it comes on while driving, that probably means your brake system is low on fluid because of a leak or a problem with the brake master cylinder. Note that this is not the same warning light that comes on when you apply the hand- or foot-operated parking brake.

All cars and light trucks also have front disc brakes. Most have rear discs, as well, though some lower-priced cars still come with rear drum brakes. With discs, it has been common practice to just replace the brake pads and resurface the rotors on a lathe if needed so the surface is even and smooth.

In recent years, however, more automakers have switched to rotors that are lighter and thinner to reduce weight and save money. Discs used to last through two or three resurfacings, but don’t be surprised if when it’s time to replace the pads you’re told you also need new rotors. The current ones may not have enough material to be shaved off in resurfacing and may not be as durable as those from, say, 10 or more years ago.

If you see different colored exhaust fumes it’s time to pay attention to your car. Even if your vehicle isn’t flashing any warning lights, the smoke coming from your exhaust is a signal that something might not be working properly.

*What does BLUE smoke from my exhaust mean?

If your car is blowing blue smoke, it’s a clear sign that the engine is burning oil. What happens is that the valve guide seals or piston rings are worn out, and oil is leaking past from where it should be lubricating the moving parts, to the combustion chamber where it’s being burned up with the fuel.

If you’re seeing this kind of smoke, check your oil regularly and watch for consumption issues. While an issue that normally should require immediate attention and expensive repairs, including some internal replacement parts, if you’re vehicle is old and the leak is minimal, it can be carefully managed by topping up the oil on a regular basis.

Along with environmental damage, burning oil can cause rough starts, as the process can ruin the car’s spark plugs.

There is another reason for blue smoke, and that’s if the car is turbocharged; the smoke being a sign that the blower is in need of rebuilding or replacement.

*What does GRAY smoke from my exhaust mean?

Gray smoke is hard to diagnose directly. Like blue smoke, it can mean that the car is burning oil or suffering from a bad turbocharger. Take the same precautions as with blue smoke, and check for excessive oil consumption.

Gray smoke can also be an issue with your automatic transmission fluid getting burned up in the engine. A faulty transmission vacuum modulator would be the culprit in this situation, leading to transmission fluid getting sucked into the engine and getting burned up.

Furthermore, gray smoke could mean a stuck PCV valve. The PCV system (Positive Crankcase Ventilation) cuts down on harmful emissions by recycling them back into the combustion chamber. However, when the PCV valve gets stuck, pressure can build and lead to oil leaks. Fortunately, PCV valves aren’t expensive, and can be a quick job for a mechanic or a do-it-yourselfer.

*What does WHITE smoke from my exhaust mean?

White smoke can be nothing to be concerned about if it’s thin, like vapor. This is probably the result of normal condensation buildup inside the exhaust system. This kind of smoke disappears quickly.

However, thicker smoke is a big problem, and can be caused the engine burning coolant. This can be the result of a serious issue like a blown head gasket, a damaged cylinder head, or a cracked engine block – all of which are costly repairs.

Don’t ignore it, however, as the problem could become far worse. Even a small leak in the coolant can lead to overheating and serious risk of damage to the engine. A coolant leak can also mix with oil and cause serious headaches for you and your car.

*What does BLACK smoke from my exhaust mean?

Black exhaust smoke means the engine is burning too much fuel. The first think you should check is your air-filter and other intake components like sensors, fuel injectors and the fuel-pressure regulator. Other reasons could be a clogged fuel return line. Black smoke is usually the easiest issue to diagnose and fix, but burning unnecessary fuel will definitely affect your fuel economy, so don’t think of avoiding this one to save money, it won’t work.

Any smoke coming from your car’s exhaust pipe is a sign that your car is in distress. Pay attention to what it needs to ensure more miles for your vehicle.